Alkyl-imidazolium templating synthesis to extra-large-pore aluminogermanosilicate zeolite IRR with enhanced Al substitution and excellent catalytic performance in bulky molecule acetalization

Extra-large-pore aluminogermanosilicate zeolite IRR with interconnected 18 × 12 × 12-ring channels was prepared within a wide range of Si/Ge and Al/(Si+Ge) ratio by using a new simple and commercial alkyl-immidazolium as template. The physicochemical properties of IRR zeolite were further characterized by the combination of several techniques, including XRD, SEM, NMR, TGA, ICP, N 2 physisorption, NH 3 -TPD etc. The results revealed that aluminum could be mostly incorporated in the framework with an obviously higher content as a result of the relatively smaller organic template used in this approach. The detemplated IRR by calcination at 550 °C in air presented excellent microporosity with the presence of 18-ring extra-large-pore opening, and considerable amount of acid sites with strong acidity. Finally, for the first time the catalytic performance of IRR zeolite, in comparison with large-pore Beta (12 × 12 × 12-ring) and extra-large-pore NUD-1 (18 × 12 × 12-ring) zeolites, were evaluated for acetalization reaction of aldehydes with triethyl ortoformate. The results showed that the catalytic activity of these three zeolites for aldehydes with different molecular size, that is heptanal and diphenylacetaldehyde, were in diametrically opposite order. IRR exhibited the highest catalytic conversion on bulky substrate diphenylacetaldehyde because its much more open channel system better facilitated the diffusion of reactants into the structure interior, where active acidic sites were located.